The goal of this paper was to make the link between sintering of a 1.6% Pt/Al2O3 catalyst and its activity for CO oxidation reaction. Thermal aging of this catalyst for different durations ranging from 15 min to 16 h, at 600 and 700 degrees C, under 7% O-2, led to a shift of the platinum particle size distributions towards larger diameters, due to sintering. These distributions were studied by transmission electron microscopy. The number and the surface average diameters of platinum particles increase from 1.3 to 8.9 nm and 2.1 to 12.8 nm, respectively, after 16 h aging at 600 degrees C. The catalytic activity for CO oxidation under different CO and O-2 inlet concentrations decreases after aging the catalyst. The light-off temperature increased by 48 degrees C when the catalyst was aged for 16 h at 600 degrees C. The CO oxidation reaction is structure sensitive with a catalytic activity increasing with the platinum particle size. To account for this size effect, two intrinsic kinetic constants, related either to platinum atoms on planar faces or atoms on edges and corners were defined. A platinum site located on I planar face was found to be 2.5 more active than a platinum site on edges or corners, whatever the temperature. The global kinetic law {r (mol m(-2) s(-1)) = 103 x exp(-64,500/RT)[O-2](0.74)[CO]-0.5)} related to a reaction occurring on a platinum atom located on planar faces allows I simulation of the CO conversion curves during a temperature ramp. Modeling of the catalytic CO conversion during a temperature ramp, using the different aged catalysts, allows prediction of the CO conversion curves over a wide range of experimental conditions. (c) 2008 Elsevier B.V. All rights reserved.